1. Field of the Invention
The present invention relates generally to a circuit breaker, and more particularly, to a circuit breaker which functions both as a circuit breaker and an electromagnetic switch.
2. Description of the Background Art
A circuit breaker is generally for protecting a current path and associated equipment against overload current or short-circuit current. If a load is switched frequently, an electromagnetic switch connected in series with a circuit breaker is provided, and the load is switched by the electromagnetic switch having a long useful life as a switch.
Three types have been conventionally known in the prior art of an apparatus formed by uniting the functions of the circuit breaker and the electromagnetic switch.
The first type is for example the one disclosed in Japanese Patent Laying-Open No. 52-132382. In the apparatus of this type, the function of the circuit breaker and the function of the electromagnetic switch are integrally combined, and contacts are separately provided each for short circuit breaking and for switching a load. Although superior in performance, the apparatus of this type is usually oversized and therefore is not economical.
The apparatus of the second type is, for example, disclosed in Japanese Patent Publication No. 39-5573. The apparatus of this type switches a load by mechanically linking an electromagnet for operation and a contact, and disconnects the linking of the mechanism when an overcurrent is generated. In other words, the linking mechanism is of trip-free system and the linking is disconnected when an overcurrent tripping device operates to cause the electromagnet for operation to part contacts. Therefore, high speed breaking is possible. However, the mechanism of this trip-free system is complicated, and a long useful life as a switch is not expected because the trip-free mechanism is operated simultaneously with the switching operation.
An apparatus of the third type is, for example, disclosed in Japanese Patent Publication No. 63-36097. The apparatus of this type has an electromagnet for operation and an electromagnet for short circuit protection, and an overcurrent tripping device. The electromagnet for operation and the electromagnet for short circuit protection both directly act upon the linking means of a contact device. The apparatus of this type is superior in switching endurance strength. Against a large current, the electromagnet for short circuit protection directly opens contacts and at the same time the overcurrent tripping device operates to cut off the excitation current from the electromagnet for operation, thereby de-energizing the electromagnet.
In the circuit breaker of the third type, however, when breaking a large current, the contacts are opened by the operation of the electromagnet for short circuit protection and the current is once broken. As the electromagnet for short circuit protection being de-energized when the current is cut off, a large current is liable to conduct once again. However, the circuit breaker is provided with a latch mechanism for preventing re-conduction of the circuit. The latch mechanism of this type does not include an automatic resetting mechanism, and, therefore, it is necessary to manually reset the latch circuit to turn on the circuit again.